This is our thermal vapor deposition chamber.We use this to deposit silver and gold films for
fabricating nanoparticle arrays using nanosphere
lithography.
This is our thermal vapor deposition chamber.
We use this to deposit silver and gold films for
fabricating nanoparticle
arrays using nanosphere
lithography.
These are the lasers that we use to
study surface-enhanced Raman spectroscopy (SERS) on our nanostructures. The
large wavelength range we have access to facilitates our investigation of the
mechanism underlying surface-enhanced spectroscopies.
This is our Nikon TE300 inverted microscope. We use this setup to study the optical properties of individual nanoparticles and nanoparticle arrays. To do Raman spectroscopy with this microscope, laser light (depicted by the green line) is focused through the microscope objective onto the sample being studied. The combination of the wave plate and polarizing beam splitter is used to control the laser power focused onto the sample. The spatial filter gives the laser beam a clean Gaussian beam profile (this facilitates focussing to the diffraction-limited spot size). Raman-scattered light is either coupled into a fiber optic and analyzed using our 0.5 meter spectrometer or focused directly onto our 0.3 m imaging spectrograph.
This view of the microscope depicts how we perform wide-field imaging of our samples. If the sample is being illuminated with laser light, a holographic notch filter is used to reject light scattered off the sample at the laser wavelength. The remaining light forms an image which can either be viewed through the microscope eyepieces or digitally captured using our extremely sensitive, thermoelectrically-cooled CCD camera attached to the front port of the microscope. Alternately, a dark-field image of the sample can be collected using the dark-field condenser to illuminate the sample (see below). This configuration allow us to collect scattering spectra and images of nanoparticles and nanoparticle arrays. For samples that scatter a lot of light, the scattering specta can be analyzed using our Ocean Optics fiber optic-coupled spectrometer. For weaker signals, we must use our more sensitive CCD detectors.
This is our 0.5 m spectrometer. Our large detector arrays allows us to collect large portions of spectra in a single exposure. Liquid nitrogen cooling greatly reduces dark counts and the back-thinned format of the array drastically increases its quantum efficiency. This is what makes our CCD detector extremely sensitive.
An alternate illumination scheme is grazing-angle incidence. By bringing in the laser beam at a very shallow angle, you greatly reduce the amount of laser light collected by the objective. This suppresses the stray light background and results in the ability to dectect lower signal strengths.
This image illustrates how dark-field illumination works. The condenser illuminates the sample with a hollow cone of light at a very high numerical aperture. Because the objective lens has a smaller numerical aperture than the condenser, none of the illumination light is directly collected by the objective. Instead, only light that is scattered by the sample can be collected. This is very useful for identifying very small particles because the background is essentially completely black. The resonant Rayleigh scattering of metal nanoparticles is an ideal system to study with this technique.
This is a color composite image of the resonant Rayleigh scattering of silver nanoparticles. The image was collected by illuminating the sample with the dark-field condenser and aquiring a red, green, and blue filtered image using our thermoelectrically cooled CCD camera.